Method of making patterns and forging dies



June 17, 1947.

o. A. WHEELON METHOD OF MAKING PATTERNS AND FORGING DIES Filed July 31, 1943 2 Sheets-Sheet 1 0/177/8 A Me/on uvmvron'.

v 6 Amok/wry June 17, 1947.. o. A. WHEELON 2 ,3

' METHOD OF MAKING PATTERNS A'ND FORGING DIES Filed July 31, 1943 2 Sheets-Sheet 2 7 29/44? 0F W may /K/ 57x14? 6.-

INVENTOR.

Patented June 1?, 194'? METHOD OF MAKING PATTERNS AND FORGING DIES Orville A. Whcelon, Pacific Palisades, Calif, as-

signor to Douglas Aircraft Company, Inc.,

Santa Monica, Calif.

Application July 31, 1943, Serial No. 497,147

13 Claims.

In die forging a part, a series of dies is employed to successively shape the part from the billet or stock piece to the finished product. Each die is formed with a cavity, the cavities so progressively differing in shape in the successively used dies that the original billet, blank or stock piece, when heated is, by a series of hammer blows, brought to the desired shape, in accordance with some condition such as a desired displacement of its molecules in various directions. The forgme my thereby be made stronger in resisting tensile and other stresses or be given some other desired quality.

It is often difilcult to determine the best form for the various cavities of the successive dies and it is sometimes necessary to make sets of dies by trial and error until a completely satisfactory forging is produced, thereby incurring considerable expense since the die blocks are very carefully formed from special steels, and the finishing of the die cavities is an expensive and laborious process.

Because of the expense, there is often a tendency to make too small a number of die cavities, as indicated by faults in the finished forging. By themethod of this invention it is possible to determine the change in shape assumed by a piece of material from the initial billet or work piece to finished forging;'and by making casts of a piece of material at different stages selected as those necessary to change the form of the material in the desired manner, to arrive at the proper number of die cavities required, their proper contours, and the most advantageous spacing of the dies relative to the sequential changes in form required; that is, to enable comparatively great changes in form to be'made in a few dies at points where it is easy for the necessary flow ofthe material to take place, and to provide more dies at points, such as when the finished form of the part is being approached, when the metal is required to fill small cavities, or form curves of small radius.

It is the general object of the invention to provide a method of producing improved dies to produce satisfactory forgings at a comparatively low cost.

An object of the invention is to provide a method of producing a die block having a plurality of die cavities each of which, except the finish die, is made from a, forged part of lastic material initially forced into the finished shape of the part while in the elastically deformable condition but not stressed beyond the elastic limit of the plastic, the plastic forging having been then reheated and allowed to recover to a determined degree of the original former the billet at which time recovery is stopped and a cast 01- the part made and used to form an intermediate or blocker die, this step-being repeated until the desired number of intermediate forms have been determined including if desired the shape of the initial forming dies known as fullering, edging, or bender dies.

Another object of the invention is to provide a method of producing aplurality of intermediate I ducting plastic material -.to render it capable of being heated by electric induction to enable material to be used in the die forming method of this invention,

A further feature of the invention is to produce forging dies accurately formed to effect the requisite change of form in the metal being forged with a minimum of displacement cfthe metal particlesin order to: reduce the wear on the die.

Still other objects of the inventionmay hereinafter appear inthe following specification.

T e method of the invention is particularly described and illustratedherein with respect to the production of :small forgedparts for airplanes; however, the scope of the invention is not Figure 3 is a view of the part after reheating the form of Figure. 2.and allowing a recovery period of four minutes.

Figure 4 is a view of the plastic part in the form of the work piece after reheating the form of Figure 3 and allowing a recovery period of nine minutes.

F gure 5 is a diagrammatic representation of 3 a flow sheet showing the successive steps in the method of my invention.

Whileforging provides arts of maximum strength, and in many cases involving quantity production, is relatively cheap, the initial cost of making the die blocks and dies makes it necessary that care be taken to insure satisfactory forgings without incurring the cost of remaking the dies to cure defects in the forgings produced.

It has hitherto been difiicult to predict, in the case of more intricate parts, whether the dies as first designed would turn out satisfactory forgings, since the behavior of the metal in thedie under the pressure of the hammer or press is not fully understoodand therefore, the produc-, tion of satisfactory forgings is largely a, matter of accumulated experience in most cases and of trial and error when forgin new materials or unusual shapes.

The method of the present invention obviates the trial and error procedure of previously used methods for formin forging dies, as it is possible with the method herein disclosed to produce prototypes of the finished part at selected stages in the forming operation without producing dies to form the prototypes. The selected prototypes can then be used to form a series of dies by which the workpiece can be progressively formed. The prototypes are formed by producing an exact replica of the part to be formed of a material which possesses the property of returning to an initial shape after it has been formed by heat and pressure. This property is known in the art as elastic memory. Material possessing this property will return toits initial shape upon reheating, and the return can be arrested by cooling the material to a temperature at which the material is rigid. As the replica in its return will follow in reverse order the changes necessary to produce the finished metal part, it is comparatively easy to select the forming contours of the die necessary to bring about the desired sequential changes in the metal during the forging operations.

The desired dies may be formed from the rigid plastic part by any suitable process known in the art. For instance, plaster casts of the part may be used to obtain sand molds which in turn can be used to form the dies by casting Kirksite around the molds to form the dies. The plaster casts, if desired, can be used as patterns to produce the dies in an automatic die-sinking or Keller machine.

The method of the present invention can be carried out by forming asingle part of the material possessing the desired property and then alternately heating and cooling the single part to form prototypes at various stages of the return of the material, which in turn are then used to form the dies necessary to produce the desired changes in the metal part. The method can also.

be carried out by forming a plurality of parts of the material in the finished die, and one part reheated and then cooled at the desired stage in its return. Anotherpart can then be reheated and maintained at the required temperature until it has reached a stage in its return beyond the arrested return of the first part which requires a die to produce the difference in shape. This procedure is repeated with the remaining parts until a part resumes the form of the original billet. The various parts in their progressively arrested return can then be used to either produce the dies necessary to progressively form a metal billet such as shown in Figure 4 t the part shown tangular billet. It is als'o advantageous that the plastic should be transparent to enable examination of the stresses in the piece to be made by projecting polarized light through the part in its rigid state or through sections cut therefrom.

These requirements are met by various syn-- thetics of which Plexiglas and Vim lite are given as those found most suitable at this time though it may be that other materials of the ethenoid and cellulosic groups mayprove equally'or more satisfactory in use. I

Plexiglas, a methyl methacrylate, has a plastic range within the elastic limit between 180 F. and 400 F., in which range it will recover to practically exact original shape from considerable deformation but it is liable to crackon curves of small radii. It can be heated by electrical induction although non-magnetic, by including iron filings in the part. In addition it can be easily worked with wood tools and is very clear and free from bubbles unless heated too highly.

Vinylite, a vinyl resinoid, has a useful plastic range within the elastic limit between 180 F. and

275 F. It will not crack as easily as Plexiglas on curves of small radius and can be more easily heated by electric induction. It can also be readily worked with wood tools.

The method of the invention will be described as performed with Plexiglas but only for the reason that this material has been more fully utilized to the present time than other plastics. In carryin out the method, however, as previously stated.

others of the materials referred to may be preferred on various grounds and the invention is therefore not limited to the particular materials described.

In the drawings only the more important changes of a piece of plastic from finished part to work piece are shown, but dies made from the illustrated forms of the plastic part result in sound and satisfactory forgings.

The drawing illustrates, referring particularly to Figure 1 thereof, a part I 0 of the desired plastic material formed from a die produced from a part milled or otherwise formed to finished dimensions. The part in was formed from the billet shown in Figure s by molding the same in the die under heat and pressure suflicient to cause the billet to take the form of the part shown in Figure 1. In the one embodiment of applicant's method, after the part ID has been formed, cooled and removed from the die, the part is again reheated to approximately 250 F. The reheatin of the part, due to the property of the material.

causes the part to begin to return to its original shape shown in Figure 4. When the part reaches a stage in its return which appears to be of such a shape as to be possible of forging to finish shape i particles in the plastic.

The part is again cooled and the necessary die produced from the same. The alternate heating and cooling is continued until the entire series of dies have been produced, or the patterns for their production made.

Inspection of the plastic part as first produced by the finish die will show whether the form of the work piece is that required to properly fill the die. It will be noted that in the case of the part illustrated, the work piece in shown in Figure 1 has been shaped to provide sufiicient material at one end to form the boss l2. Inspection of the thin flanges M will show whether there are cracks due to excessive pressure along the inside lower inside edge It of the flanges. These might also be caused by insufficient flow of the material at this point. It will be noted that by providing a blocker die of generally close dimensions to those of the finish die excessive pressures to form curves of small radii, and excessive lateral displacement of material'generally can be avoided. Reference to Figure 2 demonstrates how these conditions are met. It will be seen that the thickness of the web H3 in Figure 2 is somewhat thicker than in Figure 1 and the curves at the foot and along the top of the flanges M are of only slightly larger radius than in Figure 1,

The flow sheet of Figure 5 illustrates the successive steps of the invention in which a blank of plastic material, such as Plexiglas or Vinylite,

having the property of elastic memory is heated to forming temperature and placed in a finish die which is then closed to impart the finished shape to the blank. After the blank has been sufiiciently cooled to become rigid, it is removed from the die and reheated to a temperature at which it begins to return to its original shape. At the proper stage, recovery is arrested by cooling and the blank then constitutes a pattern, the shape of which is reproduced in the cavities of the die blocks which are to be used in the forging process.

The manner in which the plastic is heated is important since the plastic must be uniformly softened throughout its mass to insure proper flow of the material. Also, the heat must not be raised to a point at which disintegration of the plastic or formation of bubbles can take place.

Heating in an oil bath is a satisfactory method but takes longer than heating by electric induction which can be utilized in the case of plastics which are non-conducting by moulding metallic These particles become heated by eddy currents and transmit their heat throughout the plastic mass.

It is believed that the method of this invention provides an important advance in the forging art since by the use of my method a thorough investigation of the forms of the dies necessary to produce a satisfactory forging of any part can be quickly and inexpensively made and the appropriate dies produced.

I claim:

1. A method of forming a blocking die to be used with at least a finish die to progressively form a metal workpiece comprising in combination the steps of heating a homogeneous blank of plastic material having an initial shape substantially the same as a metal work piece to. be formed, said material having a high degree of deformability within its lastic limit with a high degree of recovery of its original form at a relatively higher temperature range, and having a high degree of rigidity at a temperature range lower than said higher temperature range, to a temperature in said higher range; placing said blank of heated plastic in a die corresponding to the finished shape of said Work-piece; closing said die and applying pressure thereto to form the plastic material to the shape of the desired workpiece; cooling the formed plastic material until it assumes a rigid condition; removing the cooled plastic part and heating it sufliciently to enable it to gradually recover, while substantially unconstrained toward its original form; cooling the plastic part when the recovery has brought about a transition such that the relative displacement of the metal of the workpiece necessary to form the workpiece from the shape of the part in the arrested recovery to the finish shape could be produced by a properly formed finish die; forming a forging contour on at least one die block corresponding in shape to a portion Of the partially recovered plastic part; reheating said plastic part while substantially unconstrained; cooling the reheated part when the recovery has again brought about a change in shape such that the transition to the shape of the part at its first arrested return could be produced in the metal workpiece by a :properly formed die; and forming a forging contour on at least one die block corresponding in shape to the part in the second arrested stage of its recovery.

2. A method of forming a series of dies increasingly approaching a finish die comprising in combination the steps of forming a finish die in a die block; heating a homogeneous blank of plas tic material having an initial shape substantially plying pressure thereto to form the plastic material to the shape of the finish die; cooling the formed plastic material until it has assumed its rigid condition; removing the rigid plastic piece formed by the die from the same; heating the piece, while the same is substantially unconstrained, until it begins to resume its original form; cooling the piece when it has partially recovered its original form to cause it to assume its rigid condition; forming a forging contour on at least one die block corresponding in shape to a portion of the partially recovered form of the material; repeating the step of permitting recovery and cooling of said material to determine the form, subject to necessary shrinkage allowances, of any desired number of; dies required to change the form of a piece of material from billet to finished forging; and forming a forging contour on at least one die block corresponding in shape to a portion of the partially recovered form of the material at each step.

3. A method of forming a series of forging dies to be used to progressively form a workpiece comprising the steps of: heating a homogeneous blank or plastic material having an initial shape substantially the same as a metal work piece to be formed, said material having a high degree of deformability within its elastic limit with a high degree of recovery of its original form at a relatively higher temperature range, and having a high degree of rigidity at a temperature range lower than said higher temperature range, to a temperature in said higher range; placing said blank of heated plastic in a die'corresponding the finished shape of said workpiece; closing t i and pressure thereto to form a c .7 o}? the d workpiece; cooling the formed plastic mat until it assumes a rigid condition; removing the cooled part and heating it sumciently to s me i substantially unconstrained, toward nal form; cooling the plastic part when the recovery has progressed to a desired degree; formc '2 least one die block cor responding in snape'tc a portion of the parally recovered form of the material; reheating the cooled plastic part, while the same is subti u s cause it to again gradua return towards i'oS original form; cooling the reheated plastic part when the recovery has progressed to a desired degree; and forming a forging contour on at least one die block corresponding in shape to a portion of the partially recovered form of the part.

4. A method of forming dies as set forth in claim'Z comprising in'addition: forming the blank ct plastic ma 1 before heatin' so as to insure that the material, when heated and placed in said finishing die, will properly fill said die.

5. A method of forming dies as set forth in claim ompr sing in addition: forming the blank ti be-lore heating so as to insure rial, when heated placed in said will properly fill said die.

" orrning blocking dies as set which the plastic material 2 plastic.

'orming blocking dies as set a I which the plastic material 5 a ceilulosic plastic. iethod of for.- use to progressively form a metal workpiece comthe steps of: heating a astic material having an i; the as a metal med, said material having a gree of deforrrability within its elastic l. with a deg of recovery of its origi- 1 ie at relatively higher temperature range, and having a high degree of rigidity at a temnre range lower than said higher tempertca temperature in said higher nge; placing said blank of heated plastic in a 3 corresponding to the finished shape 01 said workpiece; closing said die and applying pressu c thereto to form the plastic material to the pe of the desired workpiece; cooling the med plastic material until it assumes a rigid weir piece to be for f con ition; removin the cooled plastic part and J, g it suilic: er, while s" to enable it to gradually ta daily unconstrained, to-

rn; cooling the plastic part I has "orought about a transi- "ve displacement of the arrested stage of its recovery as to require a die to deform a workpiece from said shape to the ing a series of dies to be i ,aaaaas $5 a shape or the part at the first arrested sta e of its recovery; forming a forging contour on at least one die block corresponding in shape to the part in the second arrested stage of its recovery; repeating the steps of reheating and cooling of the part when the recovery brings about changes in shape of t part such that the transition to the shape of ice part at its previous arrested return could be produced in the metal workpiece by a. properly formed die; and forming a forging contour on at least one die block corresponding in shape to the part at each arrested stage of its recovery.

9. A method of forming a series of forging dies increasingly approaching a finish die for progressively deforming an article comprising in combination the steps of forming a finish die in a die block; heating a homogeneous blank of plastic material having an initial shape substantially the same as a metal work piece to be formed, said material having a high degree of deformability within its elastic limit with a high degree of recovery of its original form at a. higher temperature range, and a high degree of rigidity at a temperature range lower than said high temperature range, to a temperature within said higher range; placing said blank or heated plastie in said finish die; closing said die block and applying pressure thereto to form the plastic material to the shape of the finish die; cooling the formed part until it has assumed its rigid condition; heating the part, while the same is substantially unconstrained, until it begins to resume its original form; cooling the part when it has partially recovered its original form to cause it to assume its rigid condition to serve as a pattern; forming a die block corresponding in shape to at least a part of said pattern; repeating any desired number oi times the steps of heating to permit partial recovery and cooling to form sequential patterns; and forming a die block at the completion of each cooling step corresponding in shape to at least a part of the pattern resulting from such step.

10. A method of forming a forging die comprising in combination the steps of: heating a homogeneous blank formed of plastic material having an initial shape substantially the same as a metal work piece to be formed, said material having a high degree of deformability within it elastic limit with a high degree of recovery of its original form at a relatively higher temperature range, and having a high degree of rigidity at a temperature range lower than said higher temperature range, to a temperature in said higher range; placing said blank in a finish die; closing said die and applying pressure thereto to form the part to the shape of the finish die; cooling the formed part until the material thereof assumes a rigid condition; removing the part from the die and reheating it sufficiently to enable it to gradually recover, while substantially unconstrained, toward its original form; cooling the plastic part to arrest its recovery and to cause the material to harden; and forming a die having a forging contour corresponding in shape to the shape of the partially recovered, cooled, rigid part.

11..A method of forming forging dies comprising in combination the steps of: heating and forming at least one homogeneous blank of a plastic material having the property of elastic memory and having an initial shape substan-- tially the same as a metal work piece to be formed in a die having a forging contour corresponding anaaaae in shape to the shape of a finished metal part; removing said formed part of plastic material from said die after the part has cooled and hardened; reheating said part, while the same is substantially unconstrained, to cause the same to gradually return towards its original shape; an

resting the return of said part by cooling the same when the part reaches a stage in its return determined to be the desired shape of the metal part at one stage in the forging operation of the metal part; and forming a forging contour on at least one die block corresponding in shape to the partially recovered plastic part.

12. A method for forming a pattern for a forging die comprising in combination the steps of: heating a homogeneous blank of a plastic material having an initial shape substantially the same as that of a metal blank which is to be formed into a desired shape, said material having a high degree of deformability within its elastic limit with a high degree of recovery of its original form within a certain temperature range, and having a high degree of rigidity within a temperature range lower than said certain temperature range, to a temperature in said certain range; placing said blank of plastic material in a die having a forging contour such as to form said metal blank into the desired shape; closing said die and applying pressure thereto to form said plastic blank to the shape of said die; allowing the formed plastic blank to cool and harden; removing said blank from said die; reheating said cooled blank, while substantially unconstrained. to said certain temperature range whereby said plastic blank tends to return to its initial shape; and cooling the plastic blank prior to its complete return to its initial shape to cause the material to harden, whereby'the plastic blank can be used as a pattern for forming a forging contour on at least one die block corresponding in shape to the shape of the part at the arrested stage of its recovery.

13. A method for forming series of patterns for forging dies comprising in combination the steps of: heating a homogeneous blank of a plastic material having an initial shape substantially the same as that of a metal blank which is to be formed into a desired shape, said material having a high degree of deformability within its elastic limit with a high degree of recovery of its original form within a certain temperature 10 range, and having a high degree of rigidity within a temperature range lower than said .certain temperature range, to a temperature in said certain range; placing said blank of plastic material in a die having a forging contour such as to form said metal blank into the desired shape; closing said die and applying pressure thereto to form said plastic blank to the shape of said die; allowing the formed plastic blank to cool and harden; removing said blank from said die; reheating said cooled blank, while substantially unconstrained, to said certain temperature range whereby said plastic blank tends to =return to its initial shape; cooling the plastic blank prior to its complete return to its initial shape to cause the material to harden, whereby the plastic blank can be used as a pattern for forming a forging contour-on at least one die block corresponding in shape to the shape of the blank at the arrested stage of its recove y; and reheating the partially recovered plastic blank, while substantially unconstrained, to cause the same to again resume itsreturn toward its initial shape; and again cooling the plastic blank to cause it to harden and arrest its recovery after it has attained a closer approximation of its initial shape, whereby the hardened blank can be again used as a pattern to form a die having a different forging contour.

OR-VILLE A. WHEELON.

REFERENCES CITED The following references are of record in the file of this patent:

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